According to the Plath scholar Peter K Steinberg, it is completely unlike anything else she wrote before or after. “It’s an important work and different to what Plath’s readers are used to seeing,” Steinberg said. “So it’s exciting that it will shortly be available for reading and consideration.”

The story follows a young woman as her mother and father hustle her through the glittering halls of a cathedral-like station and on to a steam-filled platform before deserting her in a sinister carriage furnished with wine-coloured, plush seats. There Mary meets a kindly woman who guides her as the train speeds through dark tunnels and a bleak autumnal landscape.

In one of the corn fields a scarecrow caught her eye, crossed staves propped aslant, and the corn husks rotting under it. The dark ragged coat wavered in the wind, empty, without substance. And below the ridiculous figure black crows were strutting to and fro, pecking for grains in the dry ground.

At the station for the sixth kingdom, a conductor dressed in black escorts a pale woman off the train, despite her protests. Mary is relieved that the other passengers seem content, but their bland indifference about their final destination fills her companion with horror: “They won’t care until the time comes, in the ninth kingdom.”

Plath wrote the story in December 1952, while she was in her third year as a scholarship student at Smith College – an exciting but troubling time for Plath, according to the biographer Andrew Wilson, whose account of Plath’s early years, Mad Girl’s Love Song, was published in 2013.

“She was under a great deal of pressure, a lot of it self-inflicted,” Wilson said of this period. “She was incredibly competitive and she had always been used to being the best. Now she was surrounded by young women who were as talented as her, if not more so. She had to top up her income and so peeled potatoes and chopped vegetables in the college kitchen, and she also earned a sizeable amount of money from writing poems and stories.”

“Many of Plath’s early stories have their roots in her own life and deal with situations she herself had experienced,” Wilson added. “But this story stands out because of its daring metaphysical aspect.”

“I think Plath here is attempting to feminise and modify some biblical stories, as well as Dante’s Divine Comedy, by having Mary Ventura enact a journey by modern transport into the underworld,” Steinberg said. “Mary in the end is presented with an opportunity to release herself from a fate she did not choose.”

As a writer who was “deeply attuned to colour” from an early age, he continued, it’s no surprise the story’s details are awash in red. “She loved the colour through her life and so it’s no surprise to me to see it used so vividly and expertly in the story.”

For Wilson, Plath was not only conscious of mixing with women from more privileged backgrounds, she was also “anxious about her future. Would she be able to combine the role of a wife and mother with that of a writer? She was hugely ambitious, but often felt frustrated by the society in which she lived. She was angry about so many things – and quite rightly so.”

This is a story about women breaking out, being unconventional

The literary critic Sarah Churchwell cautioned against a narrowly biographical reading of the story, arguing that it is much more interesting as a story about the assertion of female agency, “not least because Plath works so hard to strip realistic social detail from it. She wants it to be read in archetypal terms, quite clearly: this is a story about women breaking out, being unconventional, and whether mothers will help young women do so, or whether they will acquiesce to patriarchal expectations and tell their daughters to repress their true selves.”

The story anticipates themes Plath returned to in her only novel The Bell Jar, Churchwell continued, which explores how “trying to be the ‘right’ kind of woman was soul-destroying. It’s also a book about hating your mother for trying to get you to comply. I would say this story also anticipates Plath’s use of mythical motifs and structures to suggest the universal aspect of women’s struggle with their mothers, and to suggest that is just as archetypal as men’s struggles with their fathers: this idea runs through both her poetry and her fiction.”

After graduating from Smith in 1955, Plath carried on writing both short fiction and poetry until her death in 1963. But it was only with the posthumous publication of her collection Ariel in 1965 that she was established as one of the 20th century’s most important poets.

It’s difficult to read about the opportunity for escape offered by the train’s emergency cord without thinking of another thread running through Plath’s life. According to Steinberg, by the time she submitted the story for Mademoiselle magazine in early 1953, suicide was already on her mind.

Steinberg explained that at the time of writing she was “dealing with a difficult relationship with a boyfriend, had a broken leg and was really starting to feel the strain of her courses, social life, financial issues, and an always-on-the-go lifestyle so that yes, I do think suicide was something she considered. But also, and kind of opposite, at this point she was in many ways rather far from taking that kind of action.”

While the story is “really very good” for a 20-year-old, Churchwell said, it’s unsurprising Mademoiselle turned it down: “The story’s symbolic-allegorical approach wasn’t really their style.”

Despite the resonances with Plath’s suicide and the difficult questions of forging an authentic self in the consumer world that resound both through the story and the rest of her work, Wilson detects an optimistic note.

“There is a possibility of spiritual rebirth, of comfort, of escape, of freedom,” he said, “a welcome balance in the Plath narrative which is often dominated by tales of her difficult marriage to Ted Hughes, his infidelity and her suicide”